The present invention generally relates to a rearview mirror assembly for a vehicle and to microwave antenna constructions.
Vehicle position identification systems are known and commonly used in vehicles for purposes relating to vehicle navigation and tracking systems. Currently, two such position identification systems that are in use are GPS and GLONASS, both of which utilize a constellation of satellites that transmit microwave signals towards the earth that, in turn, are received by a ground-based microwave receiver and used to determine the position of the receiver on the earth""s surface. Such systems are capable of a very high degree of accuracy. As a result, a great deal of research has been conducted to construct navigation systems that may be readily incorporated into a vehicle.
Position identification systems have also been used in vehicles with respect to communication systems, particularly emergency communication systems, whereby a vehicle occupant making an emergency call using a cellular telephone need not actually know the vehicle""s exact location in order to have emergency vehicles dispatch to that location. An example of such a system is the ONSTAR(copyright) system from General Motors Corporation. Other uses of position identification systems in vehicles include the use of position information to identify the time zone that the vehicle is currently in, and the use of such position data to determine which zone of magnetic variance the vehicle is in for purposes of calibrating an in-vehicle electronic compass. See U.S. Pat. Nos. 5,724,316 and 5,761,094, respectively.
Related U.S. Pat. Nos. 6,166,698 and 5,971,552 disclose the mounting of the microwave antenna in a rearview mirror assembly of a vehicle. As disclosed in related U.S. Pat. No. 6,166,698, it is desirable to mount the microwave antenna to the mounting bracket of an inside rearview mirror assembly so that the antenna has a clear view through the sloped front windshield of much of the sky above and in front of the vehicle. Additionally, the front windshield of the vehicle protects the antenna from dirt, moisture, snow, and humid air that may readily reach the microwave antenna and adversely affect its performance if it is mounted in a component on the exterior of the vehicle.
An inside rearview mirror assembly constructed in accordance with the teachings of U.S. Pat. No. 6,166,698 is shown in FIGS. 1-5. FIG. 1 shows the general mounting of rearview mirror assembly 10 to the inside surface of a front windshield 20 of a vehicle 25. FIGS. 2A and 2B show two different exemplary rearview mirror assembly constructions in which the microwave antenna may be mounted. More specifically, rearview mirror assembly 10a shown in FIG. 2A is designed to be mounted directly to windshield 20, whereas rearview mirror assembly 10b shown in FIG. 2B is mounted to the roof of the vehicle.
In general, rearview mirror assemblies include a mirror housing 30 that may have a wide variety of the possible designs, such as, for example, the mirror housing taught and claimed in U.S. Pat. No. 5,448,397. Rearview mirror assemblies also include a mirror 40 (FIG. 5) mounted in mirror housing 30, and a mounting bracket 35 that attaches mirror housing 30 to the vehicle. Such mounting brackets typically include a mounting foot 36 that is directly mounted to the vehicle and to a mirror stem 38 that extends between mounting foot 36 and mirror housing 30. As apparent from a comparison of FIGS. 2A and 2B, the structure of mounting foot 36 and mirror stem 38 may vary considerably from one rearview mirror assembly to the next. For example, mirror stem 38 may be pivotally mounted to mounting foot 36 as shown in FIG. 2A or fixedly attached to mounting foot 36 as shown in FIG. 2B. Additionally, mirror housing 30 is typically pivotally attached to mirror stem 38. Such pivotal attachments allow the driver to move and position the mirror so as to allow the driver to have a clear field of view towards the rear of the vehicle. The disclosed rearview mirror assembly also includes a display 45 (FIG. 5) housed within mirror housing 30 or housed within mounting foot 36.
As shown in FIGS. 3 and 4, a microwave antenna 50 is mounted within mounting foot 36 of mounting bracket 35 of rearview mirror assembly 10. As shown in FIG. 3, mounting foot 36 includes a mounting portion 52 and an antenna housing portion 54. The structure of mounting portion 52 is shown as being configured to attach to a mounting puck or button 56 that is attached to the inside surface of windshield 20 using an adhesive. Puck 56 includes an inclined edge surface 57 and a threaded aperture 58 formed in the surface of puck 56 opposite that which is adhered to windshield 20. Mounting portion 52 thus has an aperture 60 for engaging puck 56. One edge 62 of aperture 60 is a sloped profile so as to engage incline edge surface 57 of puck 56. In this manner, the size of aperture 60 is slightly smaller than the area of the surface of puck 56 that is opposite that which is secured to windshield 20. To then secure mounting portion 52 to puck 56, a set screw 66 is slid into an aperture 64 formed in mounting portion 52 and turned so as to thread into threaded aperture 58 on puck 56.
Antenna housing portion 54 of mounting foot 36 may be integrally formed with mounting portion 52 or formed as a separate component that may be attached to mounting portion 52. Antenna housing portion 54 includes an aperture 70 having a generally square, rectangular, or round shape or any other shape for accommodating the particular shape of antenna 50. Aperture 70 is provided so as to open towards windshield 20 through which microwave signals from satellites may pass to reach microwave antenna 50. Antenna 50 is preferably mounted in aperture 70 so as to be substantially parallel to, and slightly spaced apart from, the inner surface of windshield 20. The structure of antenna 50 is discussed further below.
As shown in FIG. 3, a foam pad 72 or other non-conductive substrate is placed within antenna housing portion 54 between antenna 50 and the inside surface of windshield 20. As shown in FIG. 4, antenna mounting portion 54 also includes a gasket 74 provided about the periphery of aperture 70, so as to provide for additional protection against moisture or debris coming between windshield 20 and antenna 50.
In addition to providing space for accommodating antenna 50, mounting foot 36 is configured to provide sufficient space for a receiver circuit 80 printed on a circuit board 82. Circuit board 82 is thus mounted directly behind antenna 50 in antenna mounting portion 54, so as to minimize the length of antenna connector 84 that extends between antenna 50 and printed circuit board 82.
Because receiver circuit 80 converts the signals received by antenna 50 into signals that may be transmitted over conventional wires, the information obtained from the satellite signals may be transmitted to other components in the vehicle via the vehicle bus or by discrete connections. More specifically, if a display 45 or additional circuitry, such as a control circuit for an electrochromic mirror or electronic compass, is mounted in mirror housing 30, receiver circuit 80 may be coupled to such circuitry via a connector line 85 that may be run between mounting foot 36 and mirror housing 30 outside of mirror stem 38 or internally through mirror stem 38 as disclosed in U.S. Pat. No. 5,984,482. Additionally, data processed by receiver circuit 80 may be transmitted via line 86 to other electrical systems within the vehicle. Mirror assembly 10 may include a shroud 88 that extends from mounting foot 36 to the vehicle headliner, so as to provide a covert channel for running cabling 86 between rearview mirror assembly 10 and the remainder of the vehicle.
As shown in FIGS. 3 and 4, microwave antenna 50 is constructed as a patch antenna including a dielectric substrate 90 having a layer of a conductive material provided on one side of dielectric substrate 90 so as to form a resonant patch 92. Antenna 50 further includes a layer of electrically conductive material on the opposite side of dielectric substrate 90, which forms a conductive ground plane 94 for antenna 50.
The above-described antenna mounting construction operates quite well. However, it has been discovered that there are certain circumstances in which the signal from a satellite within the field of view of antenna 50 would disappear and then reappear after the satellite moves to a new position in the sky or the vehicle moves to a new position relative to the satellite. Therefore, there exists a need for a modification to the above-described system so as to eliminate the system""s susceptibility to such blindspots.
One aspect of the present invention is to provide a microwave antenna for mounting in a vehicle where the antenna comprises a dielectric substrate, a conductive resonant patch mounted on one side of the dielectric substrate for receiving signals from a satellite, and a conductive ground plane mounted to an opposite side of the dielectric substrate. The ground plane has an area sufficiently large to shield the resonant patch from satellite signals that are reflected from a conductive component of the vehicle that would otherwise cause destructive interference with a signal received directly from a satellite.
Another aspect of the invention is to provide a mirror mounting bracket for mounting an inside rearview mirror assembly to a vehicle. The mirror mounting bracket comprises a mounting foot including a mounting portion for mounting said rearview mirror assembly to an inside surface of the front windshield of a vehicle, and an antenna housing portion abutting the inside surface of the front windshield and having an aperture opening towards the inside surface of the front windshield. The mounting bracket further comprises a stem extending between the mounting portion and a mirror housing of the rearview mirror assembly, and a microwave antenna mounted in the aperture of the antenna housing of the mounting foot. The microwave antenna including a conductive ground plane and a resonant component for receiving signals from a satellite. The ground plane is positioned in the antenna housing to shield the resonant patch from any satellite signals that are reflected from a conductive component of the vehicle.
Another aspect of the invention is to provide a mirror mounting bracket for mounting an inside rearview mirror assembly to a vehicle. The mirror mounting bracket comprises a mounting foot including a mounting portion for mounting said rearview mirror assembly to an inside surface of the front windshield of a vehicle, and an antenna housing portion abutting the inside surface of the front windshield and having an aperture opening towards the inside surface of the front windshield. The mounting bracket further comprises a stem extending between the mounting portion and a bezel of the rearview mirror assembly, and a microwave antenna mounted in the aperture of the antenna housing of the mounting foot. The microwave antenna including a conductive ground plane and a resonant component for receiving signals from a satellite. The ground plane is positioned in the antenna housing to shield the resonant patch from any satellite signals that are reflected from a conductive component of the vehicle.
An additional aspect of the present invention is to provide a method of preventing destructive interference between satellite signals reflected from conductive vehicle components and satellite signals directly received by a microwave antenna positioned in a vehicle. The method comprises the step of providing a conductive ground plane between a resonant component of the microwave antenna and any conductive vehicle component that may reflect a satellite signal towards the resonant component that would otherwise cause destructive interference with a signal received directly from a satellite.
These and other features, advantages, and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims, and appended drawings.